Is now a good time to buy a used vehicle? Or sell one? Here’s some insight on the state of the used car marketplace, along with pointers for anyone keen on buying or selling in the near future. Used car values have dipped. After reaching all-time high prices in June, the asking prices for “previously loved” vehicles have dipped nearly 7%. The drop in gas prices has caused an especially pronounced decline in prices for fuel-efficient vehicles—down 9% for compact cars, and down as much as 15% for hybrids.

Used cars are expected to keep getting cheaper. Using data from the Manheim Used Vehicle Value Index, Automotive News shows that used car prices have steadily declined for the past few months—and the trend is expected to continue through the end of 2011.

Still, demand and prices remain quite high. Throughout the recession and post-recession era, drivers have been hanging onto older vehicles longer before upgrading—one way this trend plays out is that business has been booming at auto repair shops. As consumers grew less likely to trade in cars, and as used car values soared, dealerships became more aggressive in trying to find used vehicles to buy—which would soon be flipped for quick profits. Even though used car values have declined in recent months, demand remains high among consumers and dealerships alike. The New York Times reports that dealerships are still paying substantially higher prices for used vehicles—especially highly sought-after low-mileage cars—than they were a year ago. The flip side of this is that most used cars are also being sold for much higher prices than they were a year ago. Overall, right now remains a good time to sell a used car, and a fairly expensive time to buy a used car. If the market plays out as the experts predict, however, as time passes you’ll get less when on the selling side of the equation, and you’ll pay less if buying.

Has the odometer been tampered with?AiM Mobile Inspections, which specializes in evaluating off-lease used cars, recently released a report stating an estimated 30% increase since January 2011 in the number of vehicles whose odometers have “potentially” been tampered with. That indicates quite a dramatic increase. Or does it? The strategic use of “potentially” means that these odometers haven’t necessarily been adjusted; it’s just that, based on a quick look at the evidence, it appears as if there could be a sharp increase in altered odometers. If nothing else, the report should serve as a reminder to find out for sure that the used car you’re buying isn’t more used than you thought.

Use a checklist, not your gut. Buying a new car can be complicated—and often, painful. But shopping for a used vehicle is possibly even more complex; there’s no need to check the fluids on a new car, for instance. Rather than simply kicking the tires and giving a used car a quick test drive, a thorough inspection is wise. Popular Mechanics created a handy checklist for just this purpose. Getting hold of the vehicle’s service history should eliminate questions about the car’s mileage, and should also obviously show how the car’s been maintained. And while some categories on the checklist are of minor concern (small tears on the seats are to be expected), others are probably deal breakers (fluid leaks).